This invention relates to a method of converting a fluorine-containing polymer such as, for example, polytetrafluoroethylene into a lower molecular weight polymer useful as a lubricating or releasing agent.
Relatively low molecular weight polymers of some fluorinated organic compounds are known for their excellent lubricity and untackiness, which are attributed to lowness of surface energy, and accordingly are used as lubricating agents and releasing agents. Polytetrafluoroethylene (PTFE) is a typical example of fluoropolymers used for such purposes.
One way to obtain PTFE of adequately low molecular weight is telomerization of tetrafluoroethylene, but this method involves several problems difficult to solve completely. For instance, it is difficult to control the reaction temperature and other items of the reaction conditions because of using the telogen also as a reaction medium, and therefore it is difficult to control molecular weight of the telomer. Besides, separation of the telomer from the telogen and the monomer is not easy.
Another way is to reduce the molecular weight of PTFE, which is prepared by a usual polymerization method, by controlled thermal decomposition in the presence of a catalytic substance or a degradation promoter. In this method a serious problem is generation of noxious gases of which disposal is very troublesome in industrial practice. Also it is known to accomplish cracking of PTFE by using radiation such as X-ray or gamma-ray. From an industrial point of view, however, using radiation is generally unwelcome because it is troublesome and costly.
GB-A 2,167,072 shows reducing the molecular weight of a fluorine-containing high polymer, which may be PTFE, by contact reaction of the polymer with a gas comprising a fluorine source at an elevated temperature. The fluorine source is selected from molecular fluorine, fluorides of halogens, fluorides of rare gas elements and nitrogen fluorides. In this method it is relatively easy to control the degree of reduction of the molecular weight, and by-products of the polymer decomposing reaction are entirely or mostly harmless substances. However, by this method it is difficult to reduce the molecular weight to below about 5000. Besides, usually the product of this method is in the form of a mass of wax, so that a pulverizing operation is needed to obtain a powder of a low molecular weight fluoropolymer.